Groundwater recharge areas of the Mt. Vulture volcanic aquifer by means of hydrogeochemical data and stable isotopic tracer.

Environmental isotope techniques and hydrogeochemical analysis were employed to identify the recharge area of Mt. Vulture hydrogeological basin placed along the external edge of the Apennine Chain (southern Italy). The groundwater in the studied area, meteoric in origin [1], derived from seepage rainwater flowing from the highest to the lowest altitude, through the volcanic leached host rock. The Vulture basin shows an altitude gradients of almost 1000 meters providing good conditions for application of water stable isotopes. Water sample were collected at 48 locations, for stable isotope (ä18O, äD) and major ion analysis. Seventeen springs were sampled from June 2007 to June 2008 along an altitudinal gradient between 340 masl and 1100 masl. Thirty-one groundwater samples were taken from the discharge of operating wells in the Vulture basin, located between 352 and 960 masl. Calculated recharge altitudes of studied aquifer showed that source areas of mainly precipitation recharge, estimated on the basis of the local vertical isotopic gradient (-0.17. ä18O/100; [1]), are generally located between 700 and 1200 masl. The isotope pattern of the volcanic aquifer reflects the spatial separation of different sources of recharge. Isotopic signatures in the south and north-eastern areas of the volcanic aquifer indicate a considerable recharge contribution by flow discharged from the adjacent volcanic domain and minor recharge input comes from fluvio-lacustrine deposits. The north-western sectors is the main recharge area of the most investigated sampling points. No relevant evaporation effects have been detecte